Diabetes is a major public health concern because of its increasing prevalence and associated health risks. The disease is characterized by high levels of blood glucose resulting from defects in insulin production, insulin action, or both. Two major forms of diabetes are recognized, Type 1 and Type 2. Type 1 diabetes (T1D) develops when the body's immune system destroys pancreatic beta cells, the only cells in the body that make the hormone insulin that regulates blood glucose. To survive, people with Type 1 diabetes must have insulin administered by injection or a pump. Type 2 diabetes mellitus (referred to generally as T2D) usually begins with either insulin resistance or when there is insufficient production of insulin to maintain an acceptable glucose level.
Although T2D is most commonly associated with hyperglycemia and insulin resistance, other diseases associated with T2D include hepatic insulin resistance, impaired glucose tolerance, diabetic neuropathy, diabetic nephropathy, diabetic retinopathy, obesity, dyslipidemia, hypertension, hyperinsulinemia and nonalcoholic fatty liver disease (NAFLD).
NAFLD is the hepatic manifestation of metabolic syndrome, and is a spectrum of hepatic conditions encompassing steatosis, non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and ultimately hepatocellular carcinoma. NAFLD and NASH are considered the primary fatty liver diseases as they account for the greatest proportion of individuals with elevated hepatic lipids. The severity of NAFLD/NASH is based on the presence of lipid, inflammatory cell infiltrate, hepatocyte ballooning, and the degree of fibrosis. Although not all individuals with steatosis progress to NASH, a substantial portion do.
Recent human data suggests that fructose consumption may contribute to the development of NAFLD/NASH (Vos, M. B., and Lavine, J. E. (2013, Hepatology 57, 2525-2531). Compared to glucose, fructose significantly elevates de novo lipid synthesis (Stanhope, K. L., Schwarz, et al., (2009), J Clin Invest 119, 1322-1334), a distinct characteristic of patients with NAFLD (Lambert, J. E., et al., (2014), Gastroenterology 146, 726-735). Studies in humans have demonstrated that short term fructose feeding causes increases in hepatic triglycerides and that removal of fructose consumption can reverse hepatic triglyceride accumulation (Schwarz, J. M., Noworolski, et al., (2015), J Clin Endocrino/Metab 100, 2434-2442). Moreover, in adolescents with NAFLD, 50% reduction of sugar intake for 10 days reduced hepatic triglyceride by 20% (Schwarz, J. M., Noworolski, et al., (2015) PP07-3: Isocaloric Fructose Restriction for 10 Days Reduces Hepatic De Novo Lipogenesis and Liver Fat in Obese Latino and African American Children. http://press.endocrine.org.proxy1.athensams.net/doi/abs/10.1210/endo-meetings.2015.OABA.6.PP07-3).
The high prevalence of T2D, obesity and NAFLD/NASH and associated co-morbidities, such as cardiovascular disease and stroke, has led to increased desire for both preventive care and therapeutic interventions. Current pharmacotherapies for T2D range in strategy to include agents that increase insulin secretion, impact insulin action (thiazolidinediones (TZD), biguanides), alter lipid metabolism (TZD's, fibrates), affect central-feeding behavior, promote urinary glucose excretion (SGLT2 inhibitors) and reduce nutrient absorption (lipase inhibitors). Inhibiting KHK metabolism of fructose offers a novel alternative to current treatment strategies.
Ketohexokinase (KHK) is the principle enzyme in fructose metabolism and catalyzes the conversion of fructose to fructose-1-phosphate (F1P). KHK is expressed as two alternative mRNA splice variants, denoted KHKa and KHKc, resulting from alternative splicing of the third exon. The affinity and capacity of KHKc for fructose phosphorylation is much greater than KHKa as evidenced by a much lower Km (Ishimoto, Lanaspa et al., PNAS 109, 4320-4325, 2012). While KHKa is ubiquitously expressed, the expression of KHKc is highest in the liver, kidney and intestines, the primary sites of fructose metabolism in the body (Diggle C P, et al. (2009) J Histochem Cytochem 57:763-774; Ishimoto, Lanaspa, et al., PNAS 109, 4320-4325, 2012). Additionally, loss of function mutations have been reported in humans with no adverse effects except the appearance of fructose in the urine after ingestion of the sugar.
A more severe condition involved in fructose metabolism is Hereditary Fructose Intolerance (HFI, OMIM #229600) which is caused by defects in aldolase B (GENE: ALDOB) which is the enzyme responsible for breaking down F1P and is immediately downstream of the KHK step in the pathway (Bouteldja N, et. al, J. Inherit. Metab. Dis. 2010 April; 33(2):105-12; Tolan, D R, Hum Mutat. 1995; 6(3):210-8; http://www.omim.org/entry/229600). It is a rare disorder which affects an estimated 1 in 20,000 people, and mutations result in accumulation of F1P, depletion of ATP, and increase in uric acid, the combination of which causes hypoglycemia, hyperuricemia, and lactic acidosis, among other metabolic derangements. HFI impairs the body's ability to metabolize dietary fructose resulting in acute symptoms such as vomiting, severe hypoglycemia, diarrhea, and abdominal distress, leading to long term growth defects, liver and kidney damage and potentially death (Ali M et al, J. Med. Genet. 1998 May:35(5):353-65). Patients generally suffer through the first years of life prior to diagnosis, and the only course of treatment is avoiding fructose in the diet. This is made challenging by the presence of this macronutrient in a majority of food items. In addition to physical symptoms, many patients experience emotional and social isolation as a consequence of their unusual diet, and constantly struggle to adhere to strict dietary limitations (HFI-INFO Discussion Board, http://hfiinfo.proboards.com. Accessed 14 Dec. 2015). Even when they appear non-symptomatic, some patients develop NAFLD and kidney disease, which underscores the inadequacy of self-imposed dietary restriction as the only treatment option, and the high unmet medical need for this condition.
In hyperglycemic conditions, endogenous fructose production occurs through the polyol pathway, a pathway by which glucose is converted to fructose with sorbitol as an intermediate. The activity of this pathway increases with hyperglycemia. In these studies, the authors demonstrated that the KHK null mice were protected from glucose induced weight gain, insulin resistance and hepatic steatosis suggesting that under hyperglycemic conditions, endogenously produced fructose may contribute to insulin resistance and hepatic steatosis (Lanaspa, M. A., et al., Nature Comm. 4, 2434, 2013). Therefore, the inhibition of KHK is anticipated to benefit many diseases where alterations of either or both of endogenous or ingested fructose are involved.
There remains a need for an easily administered treatment for cardiometabolic and associated diseases including diabetes (T1D and/or T2D), idiopathic T1D (Type 1 b), latent autoimmune diabetes in adults (LADA), early-onset T2D (EOD), youth-onset atypical diabetes (YOAD), maturity onset diabetes of the young (MODY), malnutrition-related diabetes, gestational diabetes, hyperglycemia, insulin resistance, hepatic insulin resistance, impaired glucose tolerance, diabetic neuropathy, diabetic nephropathy, kidney disease (e.g., acute kidney disorder, tubular dysfunction, proinflammatory changes to the proximal tubules), diabetic retinopathy, adipocyte dysfunction, visceral adipose deposition, obesity, eating disorders, excessive sugar craving, dyslipidemia (including hyperlipidemia, hypertriglyceridemia, increased total cholesterol, high LDL cholesterol, and low HDL cholesterol), hyperinsulinemia, NAFLD (including related diseases such as steatosis, NASH, fibrosis, cirrhosis, and hepatocellular carcinoma), HFI, coronary artery disease, peripheral vascular disease, hypertension, endothelial dysfunction, impaired vascular compliance, congestive heart failure, myocardial infarction (e.g. necrosis and apoptosis), stroke, hemorrhagic stroke, ischemic stroke, pulmonary hypertension, restenosis after angioplasty, intermittent claudication, post-prandial lipemia, metabolic acidosis, ketosis, arthritis, osteoporosis, left ventricular hypertrophy, peripheral arterial disease, macular degeneration, cataract, glomerulosclerosis, chronic renal failure, metabolic syndrome, syndrome X, premenstrual syndrome, angina pectoris, thrombosis, atherosclerosis, transient ischemic attacks, vascular restenosis, impaired glucose metabolism, conditions of impaired fasting plasma glucose, hyperuricemia, gout, erectile dysfunction, skin and connective tissue disorders, foot ulcerations, ulcerative colitis, hyper apo B lipoproteinemia, Alzheimer's Disease, schizophrenia, impaired cognition, inflammatory bowel disease, ulcerative colitis, Crohn's disease, and irritable bowel syndrome.